as I already stated here I got a Kwin crash (segmentation fault) when using desktop effects after I did a DU yesterday. As it looks like that had nothing do with the problem it that thread.
As I found here it is more likely a problem of the Intel graphic driver. In this article it is stated that the blur effect causes this kind of problem. Switching off the blur effect solves indeed my problem. Here my system info

I had the same problem after a dist-upgrade in the last week and disabling the Blur effect seems to solve it. Re-enabling Blur effect instantly produces a KWin crash again. The closest KDE bug report I found was this one. My backtrace with all relevant debug packages installed: